Download Development of the Brain

Chapter Five-Module 1
Development of the Brain
Chapter Fourteen-Module 1
Lateralization & Function
Development of the BrainGrowth and Differentiation of the Vertebrate Brain
Early Beginnings
 CNS begins to form at two weeks gestation
 Development of the neural tube (figure 5.2)
 At birth, brain weighs 350g, at one year
1,000g (figure 5.3)
Growth and Development of Neurons
 Proliferation-production of new cells
 Migration-move toward final destination
 Differentiation-form axons and dendrites
 Myelination-addition of insulating sheath
Figure 5.2 Early development of the human central nervous system
The brain and spinal cord begin as folding lips surrounding a fluid-filled canal. The stages shown
occur at approximately age 2 to 3 weeks.
Figure 5.3 Human brain at five stages of development
The brain already shows an adult structure at birth, although it continues to grow
during the first year or so.
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Development of the BrainNeuronal Survival
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Determinants of Neuron Survival
Must make correct connections
Must receive support from nerve growth factor
 neurotrophins act in several ways
– early in development cause cells to survive and
grow
– increase the branching of incoming axons
– decrease pain and increase regrowth of damaged
axons
apoptosis-programmed cell death that occurs when
connections are not reinforced
Competition Among Axons as a General Principle
We produce redundant synapses
the most successful axons and combinations survive
Development of the Brain
Pathfinding Axons
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Pathfinding by Axons
Chemical Pathfinding by Axons
 Example: Weiss and the grafted
salamander leg
Specificity of Axon Connections
 Example: Sperry and the rotated eye of
newt (figure)
Chemical Gradients
 cell surface molecule
 chemical attractants (e.g. TOPDV)
 Neurotrophins
Figure 5.7 Summary of Sperry’s experiment on nerve connections in newts
After he cut the optic nerve and inverted the eye, the optic nerve axons grew back to their
original targets, not to the targets corresponding to the eye’s current position.
Development of the Brain
Fine-Tuning by Experience
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Fine-Tuning by Experience
 Genetic Instruction are “only approximate”
Effects of Experience on Dendritic Branching
 Enriched environments increase dendritic branching (figure
5.10) & dendritic spine growth (5.11) thus a thicker cortex
 What is an enriched human environment? Effects?
Generation of New Neurons
 Can the adult brain generate new neurons?
 Olfactory cells must…. Why?
 stem cells in the interior of the brain
 scientists have observed new cells in hippocampus and
cerebral cortex in monkeys of ages.
 Possible meaning of new neural development?
Development of the Brain
Effects of Experience on Human Brain Structures

Example: music training on temporal lobe development
 identifying “absolute pitch” and temporal cortex growth
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Example: somatosensory cortex (post-central gyrus) in
violin players
 MEG: D5 dipole strength, age of first playing, and control
groups (figure 5.13b)
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Combinations of Chemical and Experiential Effects
 not always a clear 2-stage process of chemical pathfinding
and experiential strengthening
 e.g., the identification by lateral geniculate cells of
activating retinal neurons (spontaneous embryonic firing)
Development of the Brain
The Vulnerable Developing Brain

Fetal Alcohol Syndrome
decreased alertness, hyperactivity, varying degrees
of mental retardation, motor problems, heart defects,
and facial abnormalities

Fetal Nicotine Exposure
low birthweight, SIDS, decreased intelligence,
hyperactivity

Fetal Cocaine Exposure
decrease in IQ and language skills
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Module 1 Conclusions
Chapter Fourteen- Module 1
Lateralization
Lateralization of Function
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Some Definitions
Lateralization-Division of labor between the two
hemispheres
Commissures-Cross-over points of information in the
brain
 Corpus Callosum
 Anterior Commissure
 Hippocampal Commissure
Figure 14.1 Two views of the corpus
callosum
The corpus callosum is a large set of axons
conveying information between the two
hemispheres. (a) A sagittal section through
the human brain. (b) A dissection (viewed
from above) in which gray matter has been
removed to
expose the corpus callosum.
Figure 14.4 The anterior commissure and hippocampal commissures
These commissures allow for the exchange of information between the two
hemispheres, as does the larger corpus callosum.
Visual Connections to the Hemispheres
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Visual Field-what is visible at any moment
Right visual field-->left half of each retina-->left
hemisphere
Left visual field-->right half of each retina-->right
hemisphere
Cutting the Corpus Callosum
Sometimes done to treat severe epilepsy
Behavior is abnormal only when sensory stimuli are
limited to one side of the body
Figure 14.2 Connections from the
eyes to the human brain
Route of visual input to the two
hemispheres of the brain. Note that the
left hemisphere is connected to the left
half of each retina and thus gets visual
input from the right half of the world;
the opposite is true of the right
hemisphere.
Split Hemispheres
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Competition
Soon after surgery you may see competition
between activities on the two sides of the
body
Hemispheric Specialization
Left
 Speech
 Happiness
 Detail-oriented
Right
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Emotional content of speech
Recognizes emotions in others
Expresses fear and anger
Spatial Relationships
Music perception
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